This invention relates to the field of environmental scanning electron microscopes (ESEM), and more particularly, to an integrated electron optical/differential pumping/imaging signal detection system for an environmental scanning electron microscope.
As background, the advantages of the ESEM over the standard scanning electron microscope (SEM) lie in its ability to produce high-resolution electron images of moist or nonconductive specimens (e.g., biological materials, plastics, ceramics, fibers) which are extremely difficult to image in the usual vacuum environment of the SEM. The ESEM allows the specimen to be maintained in its "natural" state, without subjecting it to the distortions caused by drying, freezing, or vacuum coating normally required for high-vacuum electron beam observation. Also, the relatively high gas pressure easily tolerated in the ESEM specimen chamber acts effectively to dissipate the surface charge that would normally build up on a nonconductive specimen, blocking high quality image acquisition. The ESEM also permits direct, real-time observation of liquid transport, chemical reaction, solution, hydration, crystallization, and other processes occurring at relatively high vapor pressures, far above those that can be permitted in the normal SEM specimen chamber.
This technological advance in imaging capability opens a previously hidden world of microscopic phenomena to investigators in a wide spectrum of disciplines, including, but not limited to, medicine, biology, food and drug technology, geology, composite materials, textiles, semiconductors and forensics, in short, any field involving specimens which are difficult to image with the standard SEM. Previously thought impractical (if not impossible), the electron beam observation of unprepared, full-sized specimens at high vapor pressures is made possible by this invention, which combines pressure control and signal detection means, housed entirely within the magnetic objective lens of the ESEM electron beam column. This electromechanical design satisfies the simultaneous requirements for pressure control, electron beam focusing, and signal amplification, while placing no practical limitations on specimen handling or microscopic resolving power.